Group III-nitride semiconductors based on GaN have received much attention as materials for the realization of blue and green light emitting diodes. These devices are usually grown by metalorganic chemical vapor deposition (MOCVD) on sapphire or SiC substrates. On the other hand, silicon has become a desirable substrate for heteroepitaxy because of its high crystalline quality, large wafer size, low cost, and easy integration with the well-established silicon device technology. However, it is difficult to grow high quality GaN on silicon due to the large difference in lattice constant (-16.9%), crystal structure and thermal expansion coefficient (about 57%) that can result in high dislocation density. Therefore, the purpose of this study has been to investigate the crystal quality of GaN thin film on silicon substrates using GaN/AlN superlattice structures. The growth was carried out in an MOVPE system with a horizontal reactor (Aixtron 200/4 RF-S). Si(111) was chosen due to its trigonal symmetry favoring epitaxial growth of the GaN(0001) plane. Trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMIn) and ammonia (NH₃) were used as Al, Ga, In and N sources, respectively. Various GaN/AlN superlattice intermediate layer structures have been designed to decrease the threading dislocation density of GaN epilayers. The characterization techniques included TEM, SEM and double crystal X-ray diffraction. The results showed that the insertion of GaN/AlN superlattices with suitable thickness and pair combinations could be effective in reducing the etch pit density in GaN film by more than one order of magnitude. Cross-sectional transmission electron microscopy (XTEM) study confirmed the efficiency of GaN/AlN superlattice in blocking threading dislocation propagation in GaN crystal. The design of nine period GaN/AlN(20nm/2nm) superlattice has been shown to be effective in reducing the dislocation density and can improve the crystal quality. In addition, we would discuss the dislocation bending in GaN/AlN interface and dislocation merge that has become a new dislocation process.

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